The present invention relates to a communication process and apparatus for communication between communication participants. These communication participants are provided for control and/or monitoring of a technical process and are connected in communication with each other using a bus system, in particular a field bus, and can be identified using their addresses. In this process, each communication participant manages a first group of references as so-called service access points.
Communication system standard EN 50 170, Part I defines a model for managing received resources. This definition expands the source and target addresses of the associated communication participants and ultimately represents a reference that can be used to handle incoming and/or outgoing data unambiguously even with different communication relationships. IN the following, these expanded source and target addresses are designated as service access points (SAPS). For example, this means that the connection relationship which could previously be defined with the data of the sender and receiver (e.g., sender: station 1, receiver: station 3) is expanded in each case with the data for a service access point for the communication participants involved (e.g., sender: station 1.SAP3, receiver: station 3.SAP5). In this way, communication relationships to several other communication participants can be handled unambiguously for each communication participant in that each of theses communication relationships has a unique service access point made available to it.
In the majority of communication relationships, the service access points are specified implicitly through project planning for each communication relationship. In addition, there are also communication relationships in which the sender first sends a message to the potential receiver and receives an open service access point from the potential receiver as feedback. This open service access point can then be used to transfer data to the potential receiver. The actual message will then be sent to this receiver by way of the service access pint determined in this way.
However, since the number of service access points that are available per communication participant is limited, the number of possible connections that can be handled in this way is also limited by the number of service access points.
Usually, it is specified for each service access point which communication participant has the right to use that service access point. However, there can also be a specification for a service access point that it can be used by all the participating communication participants. Even if, at first glance, this increases the number of possible connections, the use of the same service access point by several communication participants in operation leads to intolerable problems.
For example, a first communication participant sends data over a service access point that is released to all communication participants and this communication participant immediately expects a response as a reaction to the data sent. This response will only be sent immediately after the data received if the response data is also immediately available. On the other hand, if the response data is not immediately available, the communication participant must inquire again at a later time as to whether the data is available. If, in the meantime, another communication participant attempts to access the same service access point, access will not be denied to it since the service access point is released to all communication participants. Instead, the data that was to be provided to the first communication participant will suddenly go to any communication participant that successfully accessed the service access point in the time between the original sending operation and the still pending receipt thereof.
Thus, it is an object of the present invention to provide a method and apparatus for expanding the connection resources that are available in a known communication process without impairing the quality and security and/or effectiveness of the communication.
These and other objects are achieved by a communication process and apparatus for communication between communication participants according to the invention. The communication participants are provided for control and/or monitoring of a technical process and are connected in communication with each other over a bus system. Each participant can be identified by an address. In the process defined by the invention, each communication participant manages a first group of references as service access points. They are managed in such a way that for at least one of the service access points a second group of references is managed, whereby access to an individual reference from this second group of references is carried out using the address of the accessing communication participant.
The first group of references (i.e. service access points) can be a group of so-called pointers, which point to a memory space that is available. Alternatively, they may comprise a field wherein each field element has a specific memory area available. In the communication process known from the above standard, the memory area that is referenced either by using the pointer or the field element can serve either directly as intermediate storage of the communication data or can contain an appropriate data structure that indicates memory areas for intermediate storage of the communication data.
The following will include a more detailed discussion of that arrangement in which the group of references is implemented as a group of pointers to memory areas. For example, if a total of five service access points are available, the resulting group of references comprises five pointers each pointing to a separate memory area. These memory areas may serve directly, or they may serve indirectly in that they reference the actual memory area by means of further pointers, in providing intermediate storage of incoming or outgoing communication data.
According to the invention, it is now provided that for at least one of the service access points, a second group of references is managed. The pointer corresponding to the service access point does not point directly to the memory area already described above. Instead, it points to a memory area which in turn, for example, contains another group of pointers. It is these further pointers that actually point to the memory areas described above. For example, if a transfer of data ensues to a first communication participant, having e.g. an address 1, by way of the service access point specified according to project planning with number 5, and the communication participant with the address 3 is sending the data, the fifth pointer (service access point 5) from the first group of references will be selected for intermediate storage of the data received. Additionally, the third pointer will be selected from the memory area that contains the second group of references, because the third pointer of this second group of references corresponds to the address 3 of the communication participant transferring the data.